Parashas Shemos
וַיֹּ֨אמֶר יְהֹוָ֤ה אֶל־מֹשֶׁה֙ בְּמִדְיָ֔ן לֵ֖ךְ שֻׁ֣ב מִצְרָ֑יִם כִּי־מֵ֙תוּ֙ כׇּל־הָ֣אֲנָשִׁ֔ים הַֽמְבַקְשִׁ֖ים אֶת־נַפְשֶֽׁךָ׃
GOD said to Moses in Midian, “Go back to Egypt, for all those who sought to kill you are dead.”
Torah Temimah points to baraisa — Nedarim 65a (verified).
ויאמר ה׳ אל משה במדין — תניא: המודר הנאה מחבירו אין מתירין לו אלא בפניו\ldots במדין נדרת לך והתר נדרך במדין.
English: “And Hashem said to Moshe in Midian” — it was taught: One who is forbidden by vow from benefit of his fellow may be released only in his presence\ldots “In Midian you vowed; go and have your vow released in Midian.”
Custom
Chazal derive that release from a vow must take place in the presence of the one to whom the vow was made.